This paper revisits the intersection of the 19th and 20th century to bring into focus hitherto unused archival and diplomatic correspondence from the attempts to define and delimit a boundary between India and China. The theoretical point of departure for the paper is to discern how perception (knowledge, beliefs, and norms) relating to the boundary evolved over time to alter the meaning and construction of the material reality i.e. the boundary itself. In doing so it establishes how what each country deems today, as its 'traditional customary boundary' was not an unambiguous fixed one, but was mutable across different time periods. The political importance of the selection of these boundary lines did not lie in their being 'true', or in the claim being 'real' but in their being shared by a process of political selection, and then being reified in the respective countries. © The Royal Asiatic Society 2017.